1. Field of the Invention
The invention relates to the field of implantable devices and more particularly to devices that are wet or heat sealed.
2. Background Information
Within the field of implantable devices, it is known to provide permeable membrane structures for implantation, the structures configured to hold drug formulations or cellular suspensions. A number of techniques have been proposed to form those structures and seal the structures. In the majority of those known techniques, the device is manufactured without the cellular suspension or drug formulation. Subsequent loading of the cellular suspension or drug formulation may occur outside a host or after the device is implanted into the host.
When a suitable cell suspension or drug formulation is loaded into the device, it is typical and frequently desireable for the permeable membrane to become wet with fluid. Given the nature of the membranes, it is known that sealing a wet membrane can be difficult or impossible. This is because known glues and solvents that are appropriate for membranes in a dry state are frequently not compatible with a wet membrane, or are toxic to cell suspensions loaded into the membrane structure. To offset this difficulty, different dry and wet seal techniques have been proposed.
In one technique, such as disclosed in U.S. Pat. No. 5,902,745 to Butler et al., the device includes a permeable tubular membrane, which is sealed with a mechanical seal after loading the device with an appropriate cell suspension. In this technique, the membrane is wet when the seal is formed, but seal integrity relies on the quality of the mechanical seal. With implantable devices, the mechanical seal dimensions are small and can be difficult to reliably manipulate. In addition, because the loading and sealing operations can be distinct, there is an opportunity for contamination of the device exterior with cells from the cell suspension after the loading operation.
In another technique, such as disclosed in U.S. Pat. Nos. 5,653,687; 5,653,688; 5,713,887; 5,738,673 and 5,932,460 issued to Mills et al, a dry seal is formed after the device is loaded. However, the loading and sealing steps are distinct and the device is open to the loading environment after loading and before the device is sealed. For some of these seals, the seal depends on mechanical aspects of the seal. Some of the disclosed seal techniques require a solvent based seal. The solvents described may be toxic to the cell suspension, however. In one particular embodiment of the seal, a portion of the device is broken off and removed after loading and prior to sealing. This action presents a strong possibility of contaminating the loading environment. This contamination can be subsequently transferred to the exterior of the device, or to other devices or apparatus.
In another technique, such as disclosed in U.S. Pat. Nos. 5,545,223 and 5,549,675 issued to Neuenfeldt et al., the apparatus or device is first implanted in a host and then loaded with a cellular suspension in the host environment. In addition to problems that are described with wet sealing of the device, this technique is performed through an incision or injection port following implantation in the host, thereby exposing the device and the host to a risk of contamination. The technique of Neuenfeldt et al. also requires a larger device to accommodate the distance between the cell suspension and the seal. This larger device also produces greater host trauma during implantation.
In some of the known techniques, the device or apparatus is loaded in an area that is remote from the host. In these methods, the loading process or apparatus provides opportunities for contamination from drug formulations or cell suspensions between the loading and the sealing steps.
As described, the methods available do not provide a secure and reliable closure system, that reduces the possibility of contamination during loading. In addition, the methods available do not provide a method to reliably seal a device after the membrane is wet. Systems and methods to address these and other deficiencies are needed.
In one aspect, the present invention provides a method of closing a containment device that comprises wetting at least a portion of a permeable polymeric membrane of the containment device with a liquid and applying heat to at least a portion of a wetted thermoplastic polymer in association with the membrane to create a closure. Such a closure is referred to herein as a xe2x80x9cwet seal.xe2x80x9d In this xe2x80x9cwet sealingxe2x80x9d process, the thermoplastic polymer melts at a lower temperature than the polymeric membrane. Once melted, the thermoplastic polymer integrates with the polymeric membrane and flows along surfaces and into available interstices of the membrane. Through passageways become filled with the melted polymer, thereby blocking fluid communication in the polymeric membrane in the region of the closure. When the thermoplastic polymer cools below its melt temperature, a closure is formed in the device. The closure is cell-tight and often liquid-tight. The portion of the device having a closure formed with a wet seal delineates a cell-impermeable region of the device.
The application of heat may be accompanied by slight pressure and a heat sink may be applied to limit heat transfer beyond the closure region to the permeable membrane. After forming the closure, the method may include pressure checking the closure integrity. The device may include additional closures that are formed by wet or dry sealing techniques.
In one aspect, the present invention provides a method of closing a containment device that comprises wetting a porous expanded polytetrafluoroethylene (ePTFE) membrane of the containment device with a liquid, and applying heat to a portion of the membrane in communication with a thermoplastic polymer, such as fluorinated ethylene propylene (FEP), to create a closure. The closure is formed by melting and fusing of the polymer to itself and the membrane in the presence of the liquid.
In one aspect, the present invention provides a method of closing a containment device comprising wetting a permeable membrane of the containment device with a liquid, wetting a thermoplastic polymer region of the device with the liquid and applying heat directly to the thermoplastic polymer region to create a closure. In this aspect, the thermoplastic polymer region is joined to the permeable membrane before wet sealing the containment device.
In one aspect, the present invention provides a method of closing a containment device that comprises applying sufficient heat to a portion of a permeable membrane in association with a thermoplastic polymer to melt and flow the thermoplastic polymer, followed by twisting the membrane/thermoplastic polymer combination in the region of the heating to form a closure. The membrane/thermoplastic polymer combination is also elongated while heating or twisting the materials. After heating, twisting, and elongation a separation region is formed and the membrane is cut in the separation region.
In one aspect, the present invention provides a containment device comprising a membrane, a polymer in communication with the membrane, and a closure. The closure is created by applying heat to a portion of the membrane and a portion of the polymer after wetting the membrane with a liquid.
In one aspect, the present invention provides a containment device comprising a membrane, a polymer region joined to the membrane and a closure. The closure is created by applying heat directly to the polymer region after wetting the membrane and the polymer region with a liquid.
In one aspect, the present invention provides a containment device comprising a membrane and a closure. The closure is created by applying heat to a portion of the membrane and twisting the membrane in the region of the heating.
In one aspect, the present invention provides a method of forming a containment device. The method comprises forming a containment region that includes a membrane, forming a thermoplastic polymer region joined to the membrane and forming a closure region. The closure region communicates with the containment region and applying heat directly to the thermoplastic polymer region after wetting the membrane creates a closure in the closure region.
In one aspect, the present invention provides a method of forming a containment device. The method comprises forming a containment region that includes a membrane, and forming a closure region. The closure region communicates with the containment region and applying heat to a portion of the membrane and twisting the membrane in the region of the heating creates a closure in the closure region.
In one aspect, the present invention provides a method of loading a containment device comprising placing a cell suspension or drug formulation in a containment region of the device through a closeable opening, the containment region including a membrane and the liquid wetting the membrane, and creating a closure in the closeable opening by applying heat to a portion of the membrane in association with a thermoplastic polymer.
In one aspect, the present invention provides a method of loading a containment device comprising creating a closed cell-tight system, the system including the containment device and a source of metabolically active cells. Loading a containment region of the device with the metabolically active cells via a closure region, the containment region including a membrane. Creating a closure at the closure region, the closure substantially or completely eliminating metabolically active cells in the vicinity of the closure, and subsequent separation of the source of cells while maintaining a closed cell-tight system.
The foregoing specific aspects, objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages that can be realized. Thus, the aspects, objects and advantages of this invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.